Study of heavy metal accumulation mechanisms in the Lachine Canal sediments

• Main Author: Galvez de Cloutier, Rosa
• Other Authors: Yong, Raymond N. (advisor)
• Format: Others
• Language: en
• Published: McGill University 1995
• Subjects: Environmental Sciences.
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29024

Due to industrialization over the past 100 years, the sediments at the bottom of the Lachine Canal and Bay have become contaminated. This study investigated the heavy metal accumulation mechanisms within the Lachine Canal sediments and was carried out in three phases. Laboratory analytical and instrumental work were included. === During Phase I, 28 parameters were measured on 44 samples collected along the Lachine Canal and Bay. The results revealed the presence of a wide variety of both organic and inorganic contaminants. Heavy metals such as Zn $>$ Pb $>$ Cr $>$ Ni $>$ Cu $>$ Cu (in order of decreasing abundance) in addition to organic contaminants (PAH $>$ MAH $>$ PCBs) were found in high concentrations exceeding background concentrations and various quality criteria levels. The total load of both organic and inorganic contaminants was found to be higher in the canal than in the bay zone. Although a positive correlation existed in between % mineral clay fraction or TOC and the total cumulative load of heavy metals, the correlation could not be assessed as conclusive. === Further study on the association heavy metal-sediment constituents (Phase II and III) was carried on the canal zone. X-ray diffraction, Transmission Electron Microscopy and other geochemical analysis revealed that the sediments consisted mainly of silt and clay size fractions composed of: illite, kaolinite and chlorite, calcite and dolomite and minor amounts of Fe- minerals, organic matter and amorphous metal oxides. Each of these constituents bound heavy metals at varying degrees as assessed by a sequential extraction (SE) protocol. The partition distribution pattern was ruled by the geochemical setting. The associations with each phase were (in order of decreasing significance): (1) residual phase Pb (50%) = Cd (50%) $>$ Cr (49%) $>$ Zn (20%), (2) oxide phase Zn (33%) $>$ Pb (32%) $>$ Cr (28%) $>$ Cd (10%), (3) carbonate phase Zn (38%) $>$ Cd (26%) $>$ Pb (13%) $>$ Cr (5%), (4) the organic phase Cr (14%) $>$ Zn (8%) $>$ Cd (6%) $>$ Pb (5%) and (5) the exchangeable phase Cd (8%) $>$ Cr (4%) $>$ Zn (1%) = Pb (1%). The order of abundance in terms of total concentration was 1300 mg Zn/kg, 500 mg Pb/kg, 90 mg Cr/kg and 10 mg Cd/kg. === According to the cation exchange capacity (CEC), carbonate and oxide content measurements, the heavy-metals occupied a minor fraction of the total capacity to retain metals by these mechanisms. The SE results revealed that the partition patterns varied with pH. The phases associated to the carbonate and the exchangeable phases were the most sensitive to a change in pH with the residual phase being almost unchanged. The Zn and Cd were sensitive to release when the conditions drifted to acidic conditions. Towards basic conditions no change in the metal distribution was observed. === The partition patterns for various grain size fractions (${}175 mu$m) revealed that no particular fraction accumulated a certain heavy metal. However, a small increment of heavy metal content with decreasing grain size was found for Zn, Pb and Cd while the contrary was found for Cr. The metal distribution of each grain size fraction followed the pattern under unsieved conditions. === Additionally, it was found that the geotechnical behaviour of sediments was influenced by the chemical composition of the sediments specially with respect to water retention.